1. Field of the Invention
The present invention relates to a liquid crystal material with optical activity, more particularly, to a liquid crystal material with strong ferroelectricity.
2. Description of Related Art
Ferroelectric liquid crystal is a material with spontaneous polarization properties, and such polarization will be inversed when an electric field is applied. The main features of liquid crystal with strong ferroelectricity include: (1) smectic liquid crystal phase with tilt angles; (2) chiral molecules (without racemic molecule) contained at the end groups of liquid crystal molecules; and (3) dipoles present at the direction perpendicular to the major axis of liquid crystal molecules. Chiral center of the compound will shorten response time. Besides, the polarity of the chiral center, rotational viscosity and electric field strength are crucial factors of the response time of ferroelectric liquid crystal.
The arrangement of molecules in ferroelectric liquid crystal is helix layer. When the molecules of two layers have the same tilt arrangement, the distance between these two layers is identified as “a pitch”. On the other hand, if the ferroelectric liquid crystal is subjected between two layers of conductive glasses wherein the distance between which is less than a pitch, the arrangement of the liquid crystal is prohibited to form helix layers. Even if the electric field is removed, the arrangement of liquid crystal before applied with electric field can't be restored anymore. Namely, the arrangement of ferroelectric liquid crystal applied with electric field can be conserved. This is so-called surface stabilized ferroelectric liquid crystal.
Furthermore, it has been proven that achiral materials with swallow-tailed groups have SmCalt phase at antiferroelectric-like structure.